The present invention relates in general to a wide range capacitive-to-digital charge balancing converter based on complementary metal-oxide-semiconductor (CMOS) devices for accurate capacitance-to-digital conversion of a capacitive sensor signal.
Capacitive sensor signal-conditioning integrated circuits, such as the cLite™ capacitive sensor signal conditioner (or cLite™ ASSP (Application Specific Standard Product)) available from Zentrum Mikroelektronik Dresden (ZMD) AG of Dresden Germany, comprise a capacitive-to-digital converter and are able to convert a capacitance within a selectable range (for example, 2-260 pF in the case of the cLite™ signal conditioner) to a corresponding digital value. Advantageously, the cLite™ signal conditioner currently provides a 14-bit resolution and very high accuracy over wide ranges of capacitances and temperatures, and can be used as input for microcontrollers or other switch applications.
Capacitive sensors are widely used in many MEMS sensing elements, such as pressure sensors for hydraulic control systems, humidity sensors and liquid level gauges. Such sensors do not touch or make direct contact with the system or device being sensed, and thus the sensors are advantageous for industrial linear and angular position sensors and contactless potentiometers, even under harsh or explosive environmental conditions.
For a capacitive-to-digital converter (CDC) covering a wide range, such as the cLite™ capacitive sensor and signal conditioner noted above, on-chip offset, reference and integrator capacitors must conventionally collectively be as large as or larger than the sensor capacitor. This can be impractical and costly depending on the desired implementation.